Violent rock slides snapped on red planet

By Richard Macey

However the sound of silence, in a world where little had been thought to change in eons, has been shattered by the rumble of rocks and ice tumbling down a 700-metre high cliff.

A NASA satellite circling the red planet has snapped the first pictures ever taken of a landslide happening on another world.

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Caught on February 19 by the space agency's Mars Reconnaissance Orbiter, the picture shows clouds of tan dust billowing into the Martian sky.

"We don't know what set off these landslides," said Patrick Russell, a member of the team that operates the spacecraft's powerful camera.

The white material at the top of the cliff, near the planet's north pole, is carbon dioxide ice. One possibility is that the spring sunshine caused blocks of the ice to expand and break apart, sending loose dust and ice particles crashing down the slope.

Alternatively, the landslides - there were at least four - could have been triggered by a "marsquake", or even a meteorite impact. The rising cloud is thought to be about 180 metres long.

Scientists have long watched the Martian polar caps grow and shrink with the seasons, and tracked dust storms that encircle the planet. NASA's robot rovers Spirit and Opportunity have even beamed back pictures of willy willies that dance across the red plains.

However the landslides are the most violent events ever observed in progress.

Glen Nagle, a spokesman for the deep space tracking station at Tidbinbilla, near Canberra, said: "The more we look at Mars, the more Earth-like it becomes, with giant volcanos, ancient dry river beds, and now spectacular avalanches."

Another member of the spacecraft's camera team, Ingrid Daubar Spitale, who was the first to spot the billowing dust in the pictures, said: "It really surprised me ... a lot of what we see there hasn't changed for millions of years."

Mr Nagle said the landslide was travelling about 15 metres a second.

Just what would a landslide on Mars sound like, in the planet's atmosphere, 100 times thinner than Earth's?

"There's been a lot of discussion about that question," Mr Nagle said.

"Depending on the amount of matter coming down, you would more likely feel it first as a low and growing rumble."

The sound would probably also be "a low and growing rumble, very similar to the sound of avalanches heard by mountaineers at the top of places like Everest and K2".

Meanwhile, space officials also have another Mars Reconnaissance Orbiter picture showing something much more familiar, but from an angle never seen by human eyes.

Shot in October, it shows a blue half Earth, hanging in a black sky below a silver moon, 142 million kilometres away.